Mixtures of saturated and unsaturated carboxylic acids are conveniently converted to products substantially free of unsaturation by means of catalytic hydrogenation. Such a process is particularly useful in the commercial production of fatty acids, compounds which are used to make base stocks for soap production, as intermediate raw materials for producing a wide range of surfactants, as foam control agents and precipitants in a variety of cleaning products, as superfatting agents in personal cleansing bars, as softener components, and for a number of other more specialized purposes. Fatty acids are obtained from fats and oils by a process the first step of which is referred to as splitting. Splitting is the hydrolysis of a fat or oil to form three molecules of fatty acid and one molecule of glycerine. The glycerine is separated and refined in a separate operation. The crude split fatty acids are usually then distilled to remove color bodies and odoriferous materials. This sequence of splitting and distilling yields the most basic tallow and coconut fatty acids which are widely used for preparing bar soaps. This basic type of coconut fatty acids also finds use in the preparation of a variety of types of surfactants. While these simple split and distilled tallow and coconut fatty acids do have wide use, many in the soap and detergents industry prefer materials with improved colors, color stabilities and odors. These improvements are often effected by hydrogenation.
In the case of tallow the hydrogenation is a partial hydrogenation. It is generally controlled so as to reduce or totally eliminate the polyunsaturated acids, which are inevitably present in split tallows. Reducing or eliminating the polyunsaturates can significantly improve the color stability of the fatty acids and many soap producers find that this carries through to improving the storage properties of their soap bars. The hydrogenation process also improves the initial color and odor of the partially hydrogenated fatty acids and this also is generally found to carry through to bar soaps. The typical catalyst used for hydrogenation is some type of nickel catalyst and it is a nonselective catalyst. That means that besides reducing polyunsaturated acids to monounsaturated acids--basically oleic acids--it also reduces some amount of unsaturated acid to saturated acid--basically stearic acid. During the hydrogenation step, oxygenated compounds such as alcohols, acids and lactones may be formed which can have a deleterious effect on products and/or processes utilizing such acids. For example, the presence of alcoholic impurities could interfere with the production of acid chlorides. It is therefore desirable to produce a hydrogenated carboxylic acid that does not contain the oxygenated compounds.